: The study of morbidity and mortality associated with air pollution historically has focused on respiratory disease. Preliminary studies by the investigators using air monitoring data together with Medicare administrative data demonstrate an association of daily levels of both carbon monoxide (CO) and airborne particulates less than 10 microns in diameter (PM10) with daily hospital admissions among Medicare recipients for cardiovascular disease. The proposed study will extend these analyses to explore the association between air pollution and cardiovascular disease and the investigate factors that may affect that association. Four specific hypotheses will be addressed. First, we propose to look at the independent and interactive effects of these pollutants on a broader range of cardiovascular conditions in eight different cities than considered in preliminary studies to determine the consistency of these relationships. Second, we will examine the modulating effect of temperature and humidity on the cardiovascular effects of these pollutants. Third, we will examine the influence of particle characteristics on the link between particulates and cardiovascular disease using detailed sampling data from Philadelphia. Finally, we will study a sub-population of Medicare beneficiaries comprised of persons with a history of hospital admissions for chronic respiratory disease to evaluate degree to which the association between cardiovascular disease and air pollution is driven by respiratory effects. Given the tremendous impact of cardiovascular disease on public health, the possibility that air pollution plays a significant role in the exacerbation of these conditions has major ramifications. The proposed research seeks to extend our knowledge concerning the health effects of air pollution in this important new direction.